1. Field of the Invention
This invention relates to a master fluid power cylinder capable of performing useful work while simultaneously controlling the coordinated operation of an associated slave cylinder which also performs useful work. In such a combination, it is often required that the pistons and the rods of the two cylinders start their movement at the same time, travel at substantially the same velocity, and reach the ends of their respective strokes at substantially the same time. This is necessary, for example, when two such cylinders are used to raise and lower opposite ends of the reel on a combine which harvests grain as it moves through the field.
Conventional master and slave cylinders can be so proportioned that they will have uniform movement. However, unequal wear of the working parts, particularly the fluid seals, causes the cylinders to get out of synchronization. They are said then to be out of phase and the operation of correcting this condition is sometimes called "rephasing".
2. Description of the Prior Art
The present state of the art on synchronizing master and slave cylinders by affording a restricted flow past the master cylinder piston at the end of the stroke is exemplified by U.S. Pat. No. RE. 28,695 issued to Evans Glenn Freese, and U.S. Pat. No. 3,832,852 issued to Loftin W. Schmucker, both of which belong to applicant's assignee.
The Freese Patent teaches a bleed orifice in the cylinder wall which passes completely through the cylinder wall into an exterior fitting or port, which is welded to the exterior of the cylinder wall. The present invention is limited to a cylinder configuration wherein the cylinder port is located in the bearing rather than welded to the cylinder wall.
The Patent to Schmucker teaches a bypass passage in the form of a groove on the inside surface of the cylinder wall extending longitudinally in the cylinder barrel. The main problem with the last mentioned longitudinal groove is that with the piston seal straddling the groove at the end of the stroke, the seal has a tendency to deform into the groove over a period of time, and when the piston is next moved, the deformed portion of the seal is sheared off.